1. Field of the Invention
This invention relates to a camera arranged to permit a slit exposure.
2. Description of the Related Art
A sequence of photographing actions of cameras practiced in general is as follows. In the case of a single-lens reflex camera, for example, when a shutter release switch is turned on, a group of leading shutter blades are allowed to travel after a mirror is moved up. Then, after the lapse of time corresponding to a set shutter time, a group of trailing shutter blades are allowed to travel to terminate an exposure of a film surface. The portion of film thus exposed is moved to a predetermined extent to permit a next shot.
The exposure of the film surface, in this case, is effected by moving a slit formed between the leading and trailing shutter blade groups with respect to a stationary surface of each of frame portions of the film. Therefore, in the event of a horse race or a car race, for example, it is only a state of one moment that can be photographed. The horses or cars which are passing a goal one after another cannot be covered by a single photograph.
To make such objects photographable, practice has been to time-serially expose the film surface for these objects by conversely arranging a slit to be stationary relative to the film surface and the film to be moved relative to the slit. Hereinafter, this exposure effecting method will be referred to as a slit exposure.
In the slit exposure, the length of film for one frame is determined by the feeding length of film and often differs from ordinary image plane sizes including 24.times.36 mm, a panorama size and a size called "high-vision" size. The shots taken by the slit exposure, therefore, are excluded from standard printing sizes and cannot be printed by ordinary low-priced standard printing service facilities. Further, ordinary standard photographic goods, such as film cases, picture frames, etc., are not usable for such shots.
It has been another problem that, in taking a shot by the slit exposure, the moving speed of a film necessary for obtaining an apposite amount of exposure is decided by computing a moving distance, on the film surface, of the object of shooting from the moving speed of the object, the object distance and the focal length of a lens in use.
Further, if the moving speed of a film varies while the slit exposure is still in process, the amount of film exposure also varies to result in an uneven exposure.